CodeViz: A CallGraph Visualiser
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README

WHERE DOES THIS CONTENT COMES FROM?
-----------------------------------
The website of codeviz was down today and It was difficult to find the source
code for download. I used:

https://web.archive.org/web/20150502053825/http://www.csn.ul.ie/~mel/projects/codeviz/#download

to find and download the source code you see here. The only change I made
was adding this header to this file.

README
------

This is the README for the CodeViz set of scripts. The tools are for
the creation of call graphs for C and C++ so that function flow can be
visualised. They are licensed under the GPL, see the COPYING file for details.

Introduction
------------

At some stage in everyone's programming career, they will need to read through
a lot of code written by another programmer. An important part of program
comprehension is building a picture of how the program is structured from
a high-level view and call graphs can be an invaluable aid when building
this piecture. This is particularly useful if the original programmer uses
clear function names. 

This project provides the ability to generate call graphs to aid the task of
understanding code. It uses a highly modular set of collection methods and
can be adapted to support any language although only C and C++ are currently
supported. Each collection method has different advantages and disadvantages.

Installing 
----------

cd codeviz
cp ./lib/* -rv /usr/lib/   (Or your preferred perl library path)
cp ./bin/* /usr/local/bin

Alternatively just run the scripts directly from the package bin/ directory
as the libraries can be found as long as the libs are installed in a global
perl directory or at the lib/ directory is the same level as bin/.

The graphs are rendered using dot which is part of the GraphViz project.
Install the package for your distribution or obtain it directly from
http://www.graphviz.org

Scripts
-------

genfull - Use this to generate the full call graph for a project. This will
	be quite large and probably should be pared down with gengraph. A
	number of collection methods are available but cdepn is the
	default. Run genfull --man to get a full man page. Do not bother
	putting the output full.graph through dot yourself as it is unlikely
	to be rendered within a reasonable amount of time

gengraph - This will generate a small subgraph and postscript file for a
	given set of functions. Run gengraph --man for full details

Generating cdepn Files for genfull
----------------------------------

If the full.graph for the source you are interested in have already been
created, you can skip this section. See ./graphs to see if a full.graph
is available.

The cobjdump and cppobjdump (for C and C++ respectively) will generate
adequate call graphs but the information is a bit lacking. For example,
the source file of a function declaration is unknown and macros and inline
functions will be totally missing. Ideally, the cdepn method should be used
but it requires a patched version of gcc and g++ to work. The patches and
some scripts are available in the compilers/ directory.

The patched version of gcc and g++ outputs .cdepn files for every c and c++
file compiled. This .cdepn file contains information such as when functions
are called, where they are declared and so on. Earlier versions of CodeViz
supported multiple gcc versions but this one only support 4.6.2.

First, the source tar has to be downloaded.  For those who have better things
to do than read the gcc install doc, just do the following

cd compilers
ncftpget ftp://ftp.gnu.org/pub/gnu/gcc/gcc-4.6.2/gcc-4.6.2.tar.gz
./install_gcc-4.6.2.sh <optional install path>

This script will untar gcc, patch it and install it to the supplied path. If
no path is given, it'll be installed to $HOME/gcc-graph . I usually install
it to /usr/local/gcc-graph with

./install_gcc-4.6.2.sh /usr/local/gcc-graph

If you seriously want to patch by hand, just read the script as it goes through
each of the steps one at a time. There is one step to note though.

For now, we will presume a patched version of gcc and g++ is now in
$HOME/gcc-graph/.  Most projects will use the variable CC for deciding
which version of gcc to use. The handiest way to use the patched one is with
something like

make CC=$HOME/gcc-graph/bin/gcc CXX=$HOME/gcc-graph/bin/g++

Or alternatively, adjust your path that gcc-graph will appear before the
normal gcc. As each source file is compiled, the corresponding cdepn file
will be created.

In the case of building the Linux Kernel, the commands would be;

make CC=$HOME/gcc-graph/bin/gcc bzImage
make CC=$HOME/gcc-graph/bin/gcc modules

Similar methods will work for other projects presuming that the Makefile
uses the CC or CXX macros correctly to indicate the compiler to use. If it's
a Makefile of your own type or it does not use proper macros, you may have
to edit the Makefile yourself or else adjust your path to put gcc-graph first.
For example, with bash, the following will work.

PATH=$HOME/gcc-graph/bin:$PATH

When building, watch the compiler output to make sure the .cdepn files are being
created.

Generating nccout files for genfull
-----------------------------------

An alternative to using a patched version of gcc is to use ncc
(http://freshmeat.net/projects/ncc) which is a C compiler specifically
designed for code browsing. It comes with it's own navigation tool and
is well worth checking out.

CodeViz supports ncc with the cncc collection method (just like cdepn is for
use with gcc) and supports C only. The really big thing going for the ncc
collection method is that it can traverse function pointers. If you download
and install ncc, use the cncc collection method if it is C code and function
pointers are common.

Once ncc is installed, in the case of building the Linux Kernel, the commands would be:

make -i CC='ncc -ncoo -ncfabs' bzImage
make -i CC='ncc -ncoo -ncfabs' modules
find . -name \*.nccout | xargs cat > code.map.nccout

Generating full.graph 
---------------------

Some full.graph files are provided with the tar in the downloads section. If
one you want is not available, read on.

To create a full.graph, the script genfull is used. run genfull --help to see
all options but the easiest thing to do is run the script with no arguments
in the top level source directory after a compile and a file full.graph will
be created in the top level source directory. 

While it should be possible to put full.graph though dot and see the postscript
file, it is recommended you do not try. A full graph is extremely large and
unlikely to be rendered in a reasonable amount of time. One really should
use the gengraph program to create smaller graphs.

Problems that might exist with full.graph
-----------------------------------------

In more complex code, the full.graph may not be perfect. For example, there may
be naming collisions where there is duplicate function names between modules or
if there is multiple binaries being compiled, genfull will not distinguish
between them. If you think this will be a problem, there is two steps you can
make.

First, compare the graph generated by cdepn with the one generated by
cobjdump. As cobjdump is analysing a binary, it is highly unlikely the graph
is wrong, it just will have no information on inline functions or macros. With
the linux kernel, this test would look something like

genfull -g cobjdump -o full.graph-objdump
genfull -g cdepn -o full.graph-cdepn
gengraph -t -d 5 -g full.graph-objdump  -f kswapd -o kswapd-objdump.ps
gengraph -t -d 5 -g full.graph-cdepn -f kswapd -o kswapd-cdepn.ps

This would generate two full.graphs and two call graphs of the function
kswapd() which could be compared to make sure the cdepn graph is accurate. A
similar method can be used for other projects.

The second problem that may occur is where function names are duplicated
between modules. In this case, the best course of action is to use the -s
switch to genfull to limit which branches of the tree are examined. For
example, in the linux kernel there is an alloc_pages() function in mm/ and
drivers/char/drm . If one was examining the VM alone and naming collisions were
expected to be a problem, genfull could be invoked as

genfull -s "mm include/linux drivers/block arch/i386"

which would cover most of the functions of interest. In other projects, it will
be a case of different libraries colliding with each other. For instance, with
avifile, genfull with no arguments will create a horrible mess. Instead, the
-s switch must be used to generate a full.graph for each part of the project.
For example, the player would be graphed with

genfull -s "player" -o full.graph-player

and each of the libraries would be graphed separately.

Generating Call Graphs 
----------------------

The script gengraph generates a call graph for a specified function based on
the full.graph file. gengraph --man will provide all the information you need.
The most important switch to note is -g which determines what collection method
to use. Once the script completes, a postscript file will be available which
can be viewed with any postscript viewer. By default, the output filename will
be functionname.ps

If it takes a long time to generate a graph, it is usually a good idea to first
limit it's depth to something reasonable with -d . We'll take an example of
graphing alloc_pages() with kernel 2.4.20

Step 1: gengraph -f alloc_pages
Result: Taking way too long, hit ctrl-c and limited by some reasonable depth to
get an idea of what was happening

Step 2: gengraph -d 10 -f alloc_pages
Result: Output graph is massive, mainly with kernel stock functions of no
interest. Use the -t switch to omit functions that are usually of no interest.
For other projects, edit the gengraph script and go to the line "sub
generate_trimlist", this function has a list of functions to "trim" with the -t
switch is used

Step 3: gengraph -t -d 10 -f alloc_pages
Result: Output graph is still massive but a glance at the graph shows that a
call to "shrink_cache()" is resulting in a massive graph below it that does not
look like it is directly related to page allocation. Lets just show that
function but not traverse it with the -s switch

Step 4: gengraph -t -d 10 -s "shrink_cache" -f alloc_pages
Result: Graph size is drastically reduced. Most of the remaining graph
involves two functions "try_to_free_pages_zone()" and "__free_pages_ok". We'll
not traverse try_to_free_pages_zone() and will ignore __free_pages_ok()
altogether with the -i switch

Step 5: gengraph -t -d 10 -s "shrink_cache try_to_free_pages_zone" -i
"__free_pages_ok" -f alloc_pages
Result: Perfect, shows a nice graph which clearly shows what the important
functions are in relation to just page allocation. Later the branches that were
not traversed in this graph can be graphed separately

The bottom line is that the first graph is usually too large and needs to be
cut down. How to pare it down in a combination of experience with the code
and common sense. I find it usually helps to just limit the depth first by
4 and start ignoring functions that are obviously not of current interest
and traverse them later

Generating Graphs based on Regular Expressions
----------------------------------------------

Support is available for selecting functions to graph, show and ignore based
on regular expressions. The format of the expression is the same as perl 
except without the //'s. For example, to generate a graph that d
that look like an alloc function in the kernel, this would work

gengraph -t -d 4 --func-re "^.?.?alloc(_page)?$" -i "pmd_alloc" -o allocs.ps

Note that with --func-re in particular, it is important that you use the -o
switch or dot will fail to create a graph with complaints about bad output
filenames.

Post-Processing Options
-----------------------

Both genfull and gengraph support the use of post-procesing steps. Currently,
two are supported. The first is stack usage by a single function.  This is x86
specific as it depends on object files regardless of the collection method
used. This is mainly of benefit to the Linux kernel as normal applications
can expand their stack and do not need to worry about stack usage as
much. The second module shows cumulative usage in gengraph between pairs of
functions. This is really handy for showing the usage between a system call
and a lower-level function to identify places where stack is used too much.

See the man pages for genfull and gengraph for more information on the use
of the post-processing options.

Daemon/Client Support
---------------------

With a large input graph, the longest operation for the generation of the call
graph is the reading of the input file. To compare, to generate a small graph
on the authors machine, it takes 4 seconds to read the input graph and 0.1
seconds to generate the output file. To address, this, gengraph can run as a
daemon if the -q (--daemon) switch is specified. Use -v if you want to see what
it is doing.

	gengraph -q -g /usr/src/linux-2.4.20-clean/full.graph

When this returns, the daemon is running. To generate a graph using the daemon,
run
	gengraph -q -t -d 2 -f alloc_pages

Note the use of the -q switch which says that gengraph should run as a client
to the daemon instance. If you are bored, compare the difference in running
times between normal gengraph and when it is used as a client :-) . To stop
the daemon, do the following

	echo QUIT > /tmp/codeviz.pipe

and the daemon will shutdown and cleanup.

Generating Graphs for the Web
-----------------------------

Gengraph is now suitable for use with CGI scripts. To generate GIF output 
instead of postfix, use the -w switch. How you choose to implement is up
to yourself but what I did was the following

o Have CGI script call gengraph to output GIF to /tmp
o In the HTML, have <img src=/cgi-bin/readgif?output.gif>

Where output.gif is actually some temporary file in /tmp created by the CGI
script with a unique name and readgif is a simply exectuable which reads
GIFs from /tmp and then unlinks them.

There is no demo of this available because the webserver which hosts this 
project is a bit loaded. While I could run a demo, my popularity would take
a bit of a dent.

There is also support for generating HTML files with source-highlight if you
have it installed. See the detailed manpage for the --shighlight option for
more details.

Misc Notes
----------

Reports of success or failure, especially with C++, using any of the collection
methods are appreciated.

Bugs and Feedback 
-----------------
Email any comments, feedback and bug reports to mel@csn.ul.ie. Enjoy.....

Credits
-------

The vast majority of this has been implemented by Mel Gorman
<mel@csn.ul.ie>.  However, the diff to gcc and original cdepn.pl that
this project was originally based on was written by Martin Devera (Devik)
(http://luxik.cdi.cz/~devik). They have since changed considerably to support
other languages and be more flexible but the original idea was his, thanks
Martin. Encouragement and prodding to support ncc is courtesy of the author
of ncc Xanthakis Stelios (sxanth@ceid.upatras.gr). The main guts of the 
implementation of the regular expression support and HTML rendering is
courtesy of Robert Lehr (bozzio@the-lehrs.com).